全文获取类型
收费全文 | 3481篇 |
免费 | 239篇 |
国内免费 | 3篇 |
出版年
2023年 | 16篇 |
2022年 | 45篇 |
2021年 | 102篇 |
2020年 | 47篇 |
2019年 | 57篇 |
2018年 | 97篇 |
2017年 | 70篇 |
2016年 | 114篇 |
2015年 | 199篇 |
2014年 | 217篇 |
2013年 | 267篇 |
2012年 | 279篇 |
2011年 | 302篇 |
2010年 | 166篇 |
2009年 | 125篇 |
2008年 | 198篇 |
2007年 | 202篇 |
2006年 | 193篇 |
2005年 | 132篇 |
2004年 | 134篇 |
2003年 | 131篇 |
2002年 | 105篇 |
2001年 | 36篇 |
2000年 | 43篇 |
1999年 | 34篇 |
1998年 | 21篇 |
1997年 | 26篇 |
1996年 | 17篇 |
1995年 | 20篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 24篇 |
1991年 | 22篇 |
1990年 | 23篇 |
1989年 | 15篇 |
1988年 | 17篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1980年 | 8篇 |
1978年 | 10篇 |
1976年 | 13篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1971年 | 7篇 |
1970年 | 8篇 |
1969年 | 10篇 |
1968年 | 10篇 |
1967年 | 7篇 |
排序方式: 共有3723条查询结果,搜索用时 15 毫秒
1.
Minh Thac Nguyen Ryan Denniston Hien Thi Thu Nguyen Tuan Anh Hoang Hana Ross Anthony D. So 《PloS one》2014,9(1)
Illicit trade carries the potential to magnify existing tobacco-related health care costs through increased availability of untaxed and inexpensive cigarettes. What is known with respect to the magnitude of illicit trade for Vietnam is produced primarily by the industry, and methodologies are typically opaque. Independent assessment of the illicit cigarette trade in Vietnam is vital to tobacco control policy. This paper measures the magnitude of illicit cigarette trade for Vietnam between 1998 and 2010 using two methods, discrepancies between legitimate domestic cigarette sales and domestic tobacco consumption estimated from surveys, and trade discrepancies as recorded by Vietnam and trade partners. The results indicate that Vietnam likely experienced net smuggling in during the period studied. With the inclusion of adjustments for survey respondent under-reporting, inward illicit trade likely occurred in three of the four years for which surveys were available. Discrepancies in trade records indicate that the value of smuggled cigarettes into Vietnam ranges from $100 million to $300 million between 2000 and 2010 and that these cigarettes primarily originate in Singapore, Hong Kong, Macao, Malaysia, and Australia. Notable differences in trends over time exist between the two methods, but by comparison, the industry estimates consistently place the magnitude of illicit trade at the upper bounds of what this study shows. The unavailability of annual, survey-based estimates of consumption may obscure the true, annual trend over time. Second, as surveys changed over time, estimates relying on them may be inconsistent with one another. Finally, these two methods measure different components of illicit trade, specifically consumption of illicit cigarettes regardless of origin and smuggling of cigarettes into a particular market. However, absent a gold standard, comparisons of different approaches to illicit trade measurement serve efforts to refine and improve measurement approaches and estimates. 相似文献
2.
Genome-wide analysis of the SET DOMAIN GROUP family in grapevine 总被引:1,自引:0,他引:1
The SET DOMAIN GROUP (SDG) proteins represent an evolutionarily-conserved family of epigenetic regulators present in eukaryotes
and are putative candidates for the catalysis of lysine methylation in histones. Plant genomes analyses of this family have
been performed in arabidopsis, maize, and rice and functional studies have shown that SDG genes are involved in the control
of plant development. In this work, we describe the identification and structural characterization of SDG genes in the Vitis vinifera genome. This analysis revealed the presence of 33 putative SDG genes that can be grouped into different classes, as it has
been previously described for plants. In addition to the SET domain, the proteins identified possessed other domains in the
different classes. As part of our study regarding the growth and development of grapevine, we selected eight genes and their
expression levels were analyzed in representative vegetative and reproductive organs of this species. The selected genes showed
different patterns of expression during inflorescence and fruit development, suggesting that they participate in these processes.
Furthermore, we showed that the expression of selected SDGs changes during viral infection, using as a model Grapevine Leafroll
Associated Virus 3-infected symptomatic grapevine leaves and fruits. Our results suggest that developmental changes caused
by this virus could be the result of alterations in SDG expression. 相似文献
3.
4.
High-resolution microscopy methods based on different nonlinear optical (NLO) contrast mechanisms are finding numerous applications in biology and medicine. While the basic implementations of these microscopy methods are relatively mature, an important direction of continuing technological innovation lies in improving the throughput of these systems. Throughput improvement is expected to be important for studying fast kinetic processes, for enabling clinical diagnosis and treatment, and for extending the field of image informatics. This review will provide an overview of the fundamental limitations on NLO microscopy throughput. We will further cover several important classes of high-throughput NLO microscope designs with discussions on their strengths and weaknesses and their key biomedical applications. Finally, this review will close with a perspective of potential future technological improvements in this field. 相似文献
5.
6.
7.
8.
M Koehler H Buba?a D Sońta-Jakimczyk E Guzikowska A Janik-Moszant M Wieczorek J Ho?owiecki 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1989,44(40-42):879-81, 884
Blasts phenotype was determined in 61 children with the acute lymphoblastic leukemia. Non-T-cell acute lymphoblastic leukemia was diagnosed in 51 children. Stages of blasts differentiation were determined with the aid of monoclonal antibodies set using alkaline phosphatase-anti-alkaline phosphatase technique. Blasts in 50 patients belonged to B subpopulation confirmed by the presence of panB CD19 and CD22 antigens. Common antigen was seen in 76.5% of the examined patients with non-T-cell acute lymphoblastic leukemia. Cases of non-T-cell acute lymphoblastic leukemia were divided into 8 subgroups depending on the antigens of B-cells differentiation. An identification of pre-B subgroups of the acute lymphoblastic leukemia indicates heterogenicity of the acute lymphoblastic leukemias in childhood and enables their classification into groups corresponding to the early stages of lymphoblasts maturation. 相似文献
9.
Narcolepsy has a 98% association with the DR2-Dw2/DQw1 haplotype. To establish if a disease-specific allele is present in narcolepsy, a cDNA library was made from a B-cell line from a DR2,4/DQw1,3 narcoleptic. Clones encoding the two expressed DR2
chains, along with DQw1 and chains, were isolated and completely sequenced. The coding regions of these four genes were similar to published nucleotide and protein sequences from corresponding healthy controls, with some minor exceptions. The 3 untranslated region of one of the DR2
genes in the narcoleptic was extended by 42 bp. Complete sequences were not available for DQw1.2 or from healthy individuals, but first domain nucleotide sequences showed only a single nonproductive difference in DQ. Partial protein sequences of both DQ and from published data were identical. Although the effects of minor differences cannot be ruled out completely, it is concluded that there are probably no narcolepsy-specific DR
or DQ / sequences, and that the alleles found in narcolepsy are representative of those found in the healthy population. 相似文献
10.